The present invention relates generally to seals and to rotary machines, and more particularly to a seal assembly having both seal teeth and brush seal bristles and to a rotary machine containing such seal.
Rotary machines include, without limitation, turbines for steam turbines and compressors and turbines for gas turbines. A steam turbine has a steam path which typically includes, in serial-flow relationship, a steam inlet, a turbine, and a steam outlet. A gas turbine has a gas path which typically includes, in serial-flow relationship, an air intake (or inlet), a compressor, a combustor, a turbine, and a gas outlet (or exhaust nozzle). Gas or steam leakage, either out of the gas or steam path or into the gas or steam path, from an area of higher pressure to an area of lower pressure, is generally undesirable. For example, gas-path leakage in the turbine or compressor area of a gas turbine, between the rotor shaft, or the rotor blade (i.e., bucket) tips, of the turbine or compressor and the circumferentially surrounding turbine or compressor casing, will lower the efficiency of the gas turbine leading to increased fuel costs. Also, steam-path leakage in the turbine area of a steam turbine, between the rotor shaft, or the rotor bucket (i.e., blade) tips, of the turbine and the circumferentially surrounding casing, will lower the efficiency of the steam turbine leading to increased fuel costs.
Steam and gas turbines have positioned a labyrinth tooth seal between the rotating rotor shaft, or the rotating bucket or blade tips, and the circumferentially surrounding stator casing to minimize fluid-path leakage. Steam and gas turbines also have positioned brush seal bristles between the rotating shaft and the circumferentially surrounding stator casing to minimize fluid-path leakage. It is known in steam and gas turbines to replace a longitudinally middle tooth of a labyrinth seal with a primary brush seal thereby creating a hybrid seal, wherein the teeth serve as a secondary seal to the better-sealing brush seal and wherein such hybrid seal is positioned between the rotating rotor shaft and the circumferentially surrounding stator casing. However, no such brush or hybrid seals are used in steam or gas turbines between the rotating bucket or blade tips and the circumferentially surrounding stator casing. It is known that the steam flow in steam turbines contains hard-water solid particles which are propelled by centrifugal force to the radially outer region of the steam path in the vicinity of the bucket tips where such fast moving particles would damage brush-seal bristles even more than they damage seal teeth. It also is known that the gas flow in aircraft gas turbines may contain foreign objects, such as runway debris, which are propelled by centrifugal force to the radially outer region of the gas path in the vicinity of the blade tips where such fast moving particles would damage brush-seal bristles even more than they damage seal teeth. What is needed is a better-sealing seal for steam and gas turbines between the rotating bucket or blade tips and the circumferentially surrounding stator casing.